One way to do it is to get a server which lets you connect via VNC or switch to web applications like google's office solutions.
AFAIK there's not one single Über-web-application for every task you might want to cover with it. You should keep in mind, that you have to use different apps hosted on different sites, if you want to go down the web-only road.
Another approach would be sharing your data via some service (or, again, your own server) that you can access from your iPad. That way you can work with a copy and sync changes back to your online storage (the "cloud").
But i wouldn't go with either approach if i were you. You'll never know where your data is stored, who as access to it and how safe they really are. What if the datacenter, where your files are stored and processed, burns down and the company you selected for hosting doesn't have off site backups (such things really happen...). IF you choose to store your data somewhere, be sure to check if you can encrypt it or encrypt it yourself.
And think of another simple scenario: What happens if you don't have web access for a few days (phone line was cut, no mobile coverage for some reason, etc). Your data is somewhere safe, but you can't work with it either.
IMHO you should keep your data where it is, maybe use the web or a server at home/offsite for backing it up and syncing with your iPad. But do not rely on 3rd parties to keep your data safe!